Stay rod assembly

ABSTRACT

A stay rod assembly for reciprocating pump assembly is disclosed. The reciprocating pump assembly includes a power section having a power source to reciprocate a plunger. A cylinder section has a chamber to receive the reciprocating plunger from the power section. The stay rod assembly secures the cylinder section to the power section. The stay rod assembly includes a stud and the sleeve. The stud has a first end, a second end, a middle portion extending between the first end the second end, and a shoulder between the first end and the middle portion. The sleeve surrounds the stud and has a first loading end adjacent the shoulder, and a second loading end adjacent the second end of the stud. The sleeve is configured to be pre-compressed and to pre-tension the stud for reducing cycling stresses.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 61/914,219 filed on Dec. 10, 2013, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

This disclosure relates to a stay rod assembly for reciprocating pumps, and more particularly, to a stay rod assembly to withstand cycling stresses typically associated with reciprocating pumps.

BACKGROUND

In oilfield operations, reciprocating pumps used for cementing, acidizing, or fracing a well typically include multiple stay rods to connect and prevent relative movement between a power end section and a fluid end or cylinder section. In operation, a plunger is reciprocatingly driven into and out of the fluid end section for pumping fluids. However, the reciprocating motion of the plunger and the associated fluid pressure variation within the fluid end section can cause substantial cycling stresses in the stay rods and ultimately lead to failure. The variation amplitudes (changes between maximum stress and minimum stress) of the cycling stresses can limit the stay rod's longevity (e.g., excessive cycling stress changes can fatigue the stay rod and develop cracks leading to structural failure). Thus, there is a need for a stay rod that to secure the power end section to the cylinder section that is capable of withstanding the cycling stresses that fatigues stay rods and leads to ultimate failure of the stay rods. This failure leads not only to damage to the pump assembly, but also costly and unanticipated downtime for the reciprocating pump.

SUMMARY

In a first aspect, there is provided a stay rod assembly for a reciprocating pump. The stay rod assembly includes a stud having a first end, a second end, and a middle portion extending between the first end and the second end. The stay rod further includes a shoulder disposed between the first end and the middle portion. The stay rod assembly also includes a sleeve surrounding the stud, the sleeve having a first loading end adjacent the shoulder and a second loading end adjacent the second end of the stud, wherein the sleeve is configured to be pre-compressed and operable to pre-tension the stud for reducing cycling stresses.

In certain embodiments, the middle portion between the shoulder and the second end further comprises a plurality of fluted channels extending at least partially therebetween for reducing the cross sectional area of the middle portion.

In other certain embodiments, the first end of the stud is secured to a power section of a reciprocating pump and the second end of the stud is secured to a cylinder section of the reciprocating pump.

In yet another embodiment, the first end is threaded and is fastened onto the power section of the reciprocating pump.

In still another embodiment, the second end is threaded to receive a nut.

In certain embodiments, the first loading end of the sleeve abuts and is pressed against the power section of the reciprocating pump when the first end of the stud is secured to the power section and the second loading end of the sleeve is pressed against a flange of the cylinder section.

In other certain embodiments, the fastener on the second end of the stay rod compresses the sleeve by a predetermined distance.

In yet other certain embodiments, the predetermined distance is between about 0.02 inches to about 0.05 inches.

In still other embodiments, the stay rod assembly further includes a first stress release groove extending at least partially around the stud and formed between the first end and the shoulder, and a second stress release groove extending at least partially around the stud and formed between the middle portion and the second end, wherein the first stress release groove and the second stress release groove each includes a corresponding gradually varying rounding radius.

In certain embodiments, the sleeve further comprises at least one visual groove indicating a correct orientation for assembling the sleeve onto the stud.

In yet another embodiment, the stay rod assembly experiences cycling stresses having a maximum stress, a minimum stress, and a difference between the maximum stress and the minimum stress, wherein the difference is no more than about 20% of the maximum stress.

In a second aspect, there is provided a reciprocating pump assembly including a power section having a power source to reciprocate a plunger, a cylinder section having a chamber to receive the reciprocating plunger, and a stay rod assembly securing the cylinder section to the power section. The stay rod assembly includes a stud having a first end, a second end, a middle portion extending between the first end and the second end, and a shoulder formed between the first end and the middle portion. The stay rod assembly further includes a sleeve surrounding the stud, the sleeve having a first loading end adjacent the shoulder and a second loading end adjacent the second end of the stud, wherein the sleeve is configured to be pre-compressed and to pre-tension the stud for reducing cycling stresses.

In certain embodiments, the middle portion further includes a plurality of fluted channels extending at least partially between the shoulder and the second end.

In other certain embodiments, the first end of the stud includes threads for fastening onto the power section of the reciprocating pump, and the second end of the stud includes threads to receive a nut.

In yet another embodiment, the first loading end of the sleeve abuts the power section of the reciprocating pump when the first end of the stud is secured to the power section and the second loading end of the sleeve abuts the cylinder section.

In still another embodiment, a fastener is disposed on the second end of the stay rod to compress the sleeve by a predetermined distance.

In other certain embodiments, the stud also includes a stress release groove extending at least partially around the stud at a position between the first end and the shoulder.

In yet another embodiment, the stud further includes a stress release groove extending at least partially around the stud at a position between the middle portion and the second end.

In certain embodiments, the stay rod assembly experiences cycling stresses having a maximum stress, a minimum stress, and a difference between the maximum stress and the minimum stress, wherein the difference between the maximum stress and the minimum stress is less than about 20% of the maximum stress.

In a third aspect, there is provided a method for assembling a reciprocating pump assembly, the pump assembly having a power section and a cylinder section and wherein the power section reciprocatingly positions a plunger toward and away from the cylinder section. The method includes securing a first end of a stud to the power section of the reciprocating pump, wherein the stud includes a middle portion extending between the first end and a second end and a shoulder positioned between the first end and the middle portion. The method further includes inserting a sleeve over the stud and pressing a first loading end of a sleeve against the power section such that the sleeve surrounds the middle portion of the stud and the first loading end is adjacent the shoulder of the stud. The method also includes inserting the second end of the stud through a flange of the cylinder section such that the second loading end of the sleeve abuts the flange of the cylinder section. The method further includes securing a fastener onto the second end of the stud such that the fastener compresses the flange and the sleeve by a predetermined distance.

In certain embodiments, the predetermined distance is between about 0.02 inches to about 0.05 inches.

In other certain embodiments, the first end and the second end of the stud comprises threads for respectively fastening to the power section and the fastener.

In yet another embodiment, the stud further includes a first stress release groove extending at least partially around the stud and located between the first end and the shoulder, and a second stress release groove extending at least partially around the stud and located between the middle portion and the second end, wherein the first stress release groove and the second stress release groove each includes a corresponding gradually varying rounding radius.

In still another embodiment, the stud and the sleeve experience cycling stresses having a maximum stress, a minimum stress, and a difference between the maximum stress and the minimum stress, and the difference between the maximum stress and the minimum stress is less than about 20% of the maximum stress.

Other aspects, features, and advantages will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are part of this disclosure and which illustrate, by way of example, principles of the disclosure.

DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view of a reciprocating pump in which a plurality of stay rod assemblies are employed to advantage.

FIG. 2 is a cross-sectional side view of the reciprocating pump of FIG. 1.

FIG. 3A is a cross-sectional side view of a stay rod assembly illustrated in FIG. 1.

FIG. 3B is a perspective view of a stud portion of the stay rod assembly of FIG. 3A.

FIG. 3C is a perspective view of a sleeve of the stay rod assembly of FIG. 3A.

FIG. 4A is a cross-sectional side view of the stud portion illustrated in FIG. 3B.

FIG. 4B is a section view of the stud illustrated in FIG. 4A taken along the line B-B of FIG. 4A.

FIG. 5A is a cross-sectional view of the sleeve illustrated in FIG. 3C.

FIG. 5B is a detailed view of a portion of the sleeve illustrated in FIG. 5A.

FIG. 6 is a cross-sectional view of the stay rod assembly's loading condition.

FIG. 7 shows calculated maximum and minimum stresses in various stay rods.

DETAILED DESCRIPTION

FIG. 1 is a perspective view of a reciprocating pump 100 in which a power end section 110 is coupled to a fluid end or cylinder section 120 via a plurality of stay rod assemblies 132 to enable a plunger assembly 130 to reciprocate into and out of the cylinder section 120. The power end section 110 is covered by a crankshaft housing 113 that shields and/or otherwise encloses the power end section 110 components. Each stay rod assembly 132 attaches to a side of the crankshaft housing 113 and extends to the cylinder section 120 thereby anchoring and/or securing the cylinder section 120 to the power end section 110. In the embodiment illustrated in FIG. 1, the cylinder section 120 includes a bank of cylinders 123, each of which are fluidly connected to a fluid inlet 129 and a fluid outlet 121. Each cylinder 123 is capped with a suction cover plate 127. In FIG. 1, three cylinders 123 are illustrated; however, a greater or fewer number of cylinders 123 may be used depending on the desired configuration.

In operation, the stay rod assemblies 132 support the cylinder section 120 by providing reaction forces against gravity, fluid pressure (e.g. transmitted through a plunger 130 and the cylinder section 120), and inertial loads of the plunger 130. During operation, a plunger 130 is reciprocatingly driven into and out of the cylinder section 120 for pumping fluids. As a result, the stay rod assemblies 132 experience cycling stresses between a maximum stress and a minimum stress, which can cause and otherwise accelerate the fatigue failure of the stay rod assemblies 132. For example, cycling stresses exceeding certain levels can initiate and propagate cracks in the stay rod assemblies 132 and lead to structural failure. In some embodiments, the cycling stresses are characterized using a ratio between the difference between the maximum and minimum stresses and the maximum stress (i.e., R=(S_(max)-S_(min))/S_(max), wherein R is the cycling stress ratio, S_(max) is the maximum stress, and S_(min) is the minimum stress). Embodiments disclosed herein provide a plurality of stay rod assemblies 132 for reduced cycling stresses such that R is not greater than about 20% thereby improving the resistance to fatigue failure by the stay rod assemblies 132. Furthermore, the stay rod assemblies 132 are configured such that cycling stresses occurring in the stay rod assemblies 132 near the power end section 110 are similar to the cycling stresses occurring in the stay rod assemblies 132 near the cylinder section 120. Such even distribution of cycling stresses oftentimes mitigate the failure of the stay rod assemblies 132 at a particular end (i.e., of the power end section 110 or the cylinder section 120).

Referring to FIG. 2, the crankshaft housing 113 houses a crankshaft 210 that is mechanically connected to a reduction gear 205 coupled to a power gear 203. In some embodiments, the crankshaft 210 operates each cylinder 123 to pump fluids at alternating times. In the embodiment illustrated in FIG. 2, a connecting rod 217 connects the crankshaft 210 to a crosshead 220 through a crosshead pin 219. The connecting rod 217 is pivotable about the crosshead pin 219 as the crankshaft 210 rotates with the opposite end of the connecting rod 217. A plunger rod 223 extends from the crosshead 220 to the plunger 225 in a longitudinally opposite direction from the crankshaft 210. During operation, the connecting rod 217 and the crosshead 220 convert rotational movement of the crankshaft 210 into longitudinal movement of the plunger rod 223 to facilitate the reciprocating movement of the plunger 225 into and out of the cylinder section 120.

In FIG. 2, the cylinder 123 includes an interior or cylinder chamber 230, in which the plunger 225 pressurizes the fluid being pumped by the reciprocating pump 100. Cylinder 123 further includes an inlet valve 240 and an outlet valve 233, both of which can be spring-loaded valves actuated by a pre-determined differential pressure. The inlet valve 240 actuates to control fluid flow through the fluid inlet 129 into the cylinder chamber 230. The outlet valve 233 actuates to control fluid flow through the fluid outlet 121 from the cylinder chamber 230.

During operation, as the plunger 225 moves away from the cylinder 123, the fluid pressure in the cylinder chamber 230 decreases creating a pressure difference across the inlet valve 240. This pressure difference opens the inlet valve 240 to allow the fluid to enter the cylinder chamber 230 from the inlet 129. The fluid enters the cylinder chamber 230 as the plunger 225 continues to move longitudinally away from the cylinder 123 until the pressure difference between the fluid inside the chamber 230 and the fluid in the fluid inlet 129 equalizes and the inlet valve 240 returns to its closed position.

When the plunger 225 reverses direction and moves toward the cylinder 123, the fluid pressure inside the cylinder chamber 230 increases and creates a pressure difference across the outlet valve 233. Before the outlet valve 233 opens, however, the fluid pressure in the chamber 230 continues to increase as the plunger 225 approaches the cylinder 123 until the pressure difference is large enough to actuate the outlet valve 233 and enable fluid to exit the cylinder 123 through the fluid outlet 121. In some embodiments, fluid is pumped across one side of plunger 225 (e.g., single acting); in other instances (not shown), fluid is pumped across both sides of plunger 225 (e.g., double acting).

During operation, movement of the plunger 225 and the associated pressure variation oftentimes results in cycling stresses in the stay rod assemblies 132. For example, the stay rod assemblies 132 are tensioned by the cylinder section 120 when the plunger 225 travels toward the cylinder chamber 230, and the stay rod assemblies 132 are compressed when the plunger 225 travels away from the cylinder chamber 230. Accordingly, the stay rod assembly 132 is provided to reduce the cycling stresses as described in greater detail below.

Referring to FIGS. 3A-3C, the stay rod assembly 132 includes a stud portion 310 and a sleeve 320. When installed, a flange 330 or other portion of the cylinder section 120 (e.g., wall, enclosure, fluid end housing, etc.) is sandwiched between the sleeve 320 and a nut 340. Referring specifically to FIGS. 3B and 3C, the stud 310 and the sleeve 320 are formed of cylindrical shapes having generally circular cross-sections and sized such that at least a portion of the stud 310 is supported within the sleeve 320. However in other implementations, the stud 310 and the sleeve 320 are configured to have a different cross-sectional geometry, such as a rectangle, a square, a “T” shape, a “U” shape, an “I” shape, a polygon, and an ellipse, or other suitable shapes.

Referring specifically to FIG. 4A, the stud 310 includes a first end 412, a second and opposed end 414 and a middle portion 417 extending between the first and second ends 412 and 414. Referring specifically to FIG, 4A, the stud 310 further includes a shoulder 425 positioned between the first end 412 and the middle portion 417. As discussed in greater detail below, the first end 412 is preferably securable to the power end section 110 of the reciprocating pump 100 (FIG. 1) and the second end 414 is otherwise securable to the cylinder section 120 via a nut 340.

In the embodiment illustrated in FIGS. 4A and 4B, the middle portion 417 includes a plurality of fluted channels 427 separated by a plurality of ridges 405. As illustrated, the fluted channels 427 (six illustrated in FIG. 4B) reduce the cross-sectional area of the middle portion 417, which reduces the overall weight and required material (as to be comparable to other stay rods commonly in use). When the first end 412 of the stud 310 is secured to the power end section 110, the shoulder 425 is pressed against the power end section 110. As such, the shoulder 425 defines a starting point for a predetermined assembly distance between the cylinder section 120 and the power end section 110. For example, the predetermined assembly distance is a pre-compressed total length of the sleeve 320.

In some embodiments, the stud 310 includes a first stress release groove 413 extending at least partially around the stud 310 and is located between the first end 412 and the shoulder 425. The stud further includes a second stress release groove 415 extending at least partially around the stud 310 and located between the middle portion 417 and the second end 414. Both the first and second stress release grooves 413 and 415 include a curved or rounded cross section along its length and reduce stress concentrations thereby allowing a more uniform distribution of stresses; however, other cross-sectional shapes may be used.

In the embodiment illustrated in FIG. 4A, the stud 310 includes machining centers 401 and 402, which are used to turn and/or otherwise rotate the stud 310 during manufacture. However in other implementations, the stud 310 is produced using different manufacturing techniques, such as for example, by casting, forging, printing, milling or any other method that does not require rotation and thus, the machining centers 401 and 402 may not be included or may have a profile suitable for use with the manufacturing technique.

According to embodiments disclosed herein, the first end 412 is securable to the power end section 110 by threads; however, other methods of attachment are available. For example, the first end 412 is securable to the power end section 110 by, for example and not by way of limitation, fusing, adhering, using one or more set screws or any combinations thereof. Similarly, the second end 414 is securable to the flange 330 (or any other portion of the cylinder section 120 without using the nut 340. For example, a set screw, a wedge, or other suitable fasteners may be used in the place of the nut 340.

Referring specifically to FIGS. 4A and 5A, the sleeve 320 includes a first loading end 540 adjacent the shoulder 425 of the stud 310 and a second loading end 520 adjacent the second end 414 of the stud 310. The sleeve 320 includes an outer surface 510 and an inner surface 530, both of which define a general wall thickness. As illustrated in FIGS. 3A and 5A, a shoulder adapter 555 reduces the wall thickness to allow the sleeve 320 to envelope or otherwise surround the shoulder 425 of the stud 310 when the sleeve 320 is installed.

During installation, the sleeve 320 is configured to be pre-compressed between the power end section 110 and the cylinder section 120. For example, during installation, the nut 340 on the second end 414 is tightened to move the flange 330 a distance between about 0.02 inches and 0.05 inches toward and to otherwise compress the sleeve 320. This movement causes the sleeve 320 to tension the stud 310, which achieves a reduced cycling stress magnitude. For example, the stay rod assembly 132 experiences cycling stresses that have a maximum stress and a minimum stress. The cycling stress magnitude is reflected by the ratio between a difference between the maximum stress and the minimum stress, and the maximum stress. In the embodiment shown in FIG. 3A, the difference between the maximum stress and the minimum stress is no more than about 20% of the maximum stress.

Referring specifically to FIG. 5B, the sleeve 320 includes a first visual indicator 560 and a second visual indicator 562 to indicate to an installer the correct orientation for assembling the sleeve 320 onto the stud 310. For example, the visual indicators 560 and 562 identify the first loading end 540 near which the shoulder adapter 555 is located such that the first loading end 540 directly contacts the power end section 110 without interfering with the shoulder 425 of the stud 310. In the embodiment illustrated in FIG. 5B, the visual indicators 560 and 562 are grooves that extend around the sleeve 320; however, other configurations may be used. For example, the visual indictors alternatively may include labels, decals, painted markers, laser engravings, RFIDs (radio frequency identifiers) and other indicator or combination thereof. Furthermore, while two visual indicators 560 and 562 are illustrated in FIG. 5B, it should be understood that a greater or fewer number of visual indicators 560, 563 can be used.

In some embodiments, the stud 310 extends a length of 19.5 inches machined from a rolled rod of 1.75 inches in diameter. The sleeve 320 has a total length of 13 inches, an inner diameter of 1.775 inches for surrounding the stud 310, and an outer diameter of 2.755 inches for providing a wall thickness of 0.5″. The shoulder adapter 555 is configured to reduce the wall thickness to 0.3 inches for 0.5 inches in length to adapt to the shoulder 425 that is 0.39 inches in length. A distance of 2 inches exists between the shoulder 425 and the first end 412. The first stress release groove 413 is 0.5 inches from the first end 412. The ridges 405 can be at least about 10 inches in length. The second end 414 can be at least 2.38 inches in length and threaded with a 1.6665 to 1.6590 pitch diameter.

FIG. 6 is a cross-sectional side view of the stay rod assembly 132 in a loaded configuration. In FIG. 6, the cross-sectional side view illustrates a sixth of a model of the stay rod assembly 132. Correspondingly, a sixth of applied loads (e.g., 11375 lbf, under the assumption of having four stay rod assemblies supporting the cylinder section 120) are applied in an analysis for the stay rod assembly 132. In this model, the nut 340 is modeled being integrated with the stud 310 for representing the tightened threaded engagement. The first end 412 of the stud 310 is secured to the power end section 110 and experiences a support loading 610 in both the axial and lateral directions. An axial support load 612 is provided from the power end section 110 to the first loading end 520 of the sleeve 320. The sleeve 320 transfers the axial support load 612 to the flange 330 as a compressive load 620, which partially transfers to the nut 340 as a reaction load 623.

When installed, the stay rod assembly 132 has the nut 340 tightened such that the sleeve 320 is compressed by a predetermined distance and the stud 310 is pre-tensioned as a result. This compression and pre-tensioning reduces the cycling stresses in terms of a ratio between the difference of the maximum stress and the minimum stress and the maximum stress. The reduced ratio mitigates fatigues in the stay rod assembly and the associated fatigue related structural failure. For example, the sleeve 320 can be compressed for a predetermined distance between about 0.02 inches to about 0.05 inches, such as 0.038 inches. The predetermined distance is calculated from the sum of stay rod elongation and sleeve compression incurred by resultant axial force of the torque applied to the nut 340.

The analysis modeled in FIG. 6 is an exemplary embodiment of a simulated result having a stress of 79,664 psi at the first stress release groove 413 near the power end section 110, and a stress of 74,710 psi at the second stress release groove 415 near the cylinder section 120. A stress of 67,560 psi is in the middle portion 417. These stresses are within design range below the yield strength of the selected material of the stay rod assembly 132. In this analysis, the stress of 79,664 psi is the maximum stress experienced in the stay rod assembly 132 near the power end section 110; and the stress of 74,710 psi is the maximum stress experienced in the stay rod assembly 132 near the cylinder section 120, as also presented in FIG. 7 below.

FIG. 7 is an exemplary embodiment of calculated maximum and minimum stresses of various stay rods during operation. The results of the stay rod assembly 132 are presented in column 730 near the cylinder section 120 and in column 732 near the power end section 110. The x axis 715 shows three different stay rods' cycling stresses at both ends near the cylinder section and the power section. The y axis 710 shows the normalized cycling stresses in terms of ratios between the difference between the maximum stress and the minimum stress, and the maximum stress, wherein the maximum stresses and minimum stresses of the three stay rods are presented in the table 720. The comparison presented in FIG. 7 shows that stay rods other than the stay rod assembly 132 have much smaller cycling stress ratios (i.e., 10% for the 2250 stay rod, and 47% for the 2400 stay rod) near the cylinder section 120 than the cycling stress ratios (i.e., 62% for the 2250 stay rod, and 61% for the 2400 stay rod) near the power section. The stay rod assembly 132 shows an even distribution of the cycling stress ratios (i.e., both about 19%). More importantly, the cycling stress ratios of the stay rod assembly 132 are less than a third (19%) of the maximum ratio (62%) of the other stay rods. This improved performance for the stay rod assembly 132 can significantly improve resistance against fatigue.

In the foregoing description of certain embodiments, specific terminology has been resorted to for the sake of clarity. However, the disclosure is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes other technical equivalents which operate in a similar manner to accomplish a similar technical purpose. Terms such as “left” and “right”, “front” and “rear”, “above” and “below” and the like are used as words of convenience to provide reference points and are not to be construed as limiting terms.

In this specification, the word “comprising” is to be understood in its “open” sense, that is, in the sense of “including”, and thus not limited to its “closed” sense, that is the sense of “consisting only of”. A corresponding meaning is to be attributed to the corresponding words “comprise”, “comprised” and “comprises” where they appear.

In addition, the foregoing describes some embodiments of the disclosure, and alterations, modifications, additions and/or changes can be made thereto without departing from the scope and spirit of the disclosed embodiments, the embodiments being illustrative and not restrictive.

Furthermore, the disclosure is not to be limited to the illustrated implementations, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the disclosure. Also, the various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment may be combined with aspects of another embodiment to realize yet other embodiments. Further, each independent feature or component of any given assembly may constitute an additional embodiment. 

What is claimed is:
 1. A stay rod assembly comprising: a stud having a first end and a second end, a middle portion extending between the first end and the second end, and a shoulder between the first end and the middle portion; and a sleeve surrounding the stud, the sleeve having a first loading end adjacent the shoulder and a second loading end adjacent the second end of the stud, wherein the sleeve is configured to be pre-compressed and to pre-tension the stud for reducing cycling stresses.
 2. The stay rod assembly of claim 1, wherein the middle portion between the shoulder and the second end further comprises a plurality of fluted channels for reducing a cross sectional area of the middle portion.
 3. The stay rod assembly of claim 1, wherein the first end of the stud is secured to a power section of a reciprocating pump and the second end of the stud is secured to a cylinder section of the reciprocating pump.
 4. The stay rod assembly of claim 3, wherein the first end is threaded and is fastened onto the power section of the reciprocating pump.
 5. The stay rod assembly of claim 3, wherein the second end is threaded to receive a nut.
 6. The stay rod assembly of claim 3, wherein the first loading end of the sleeve is pressed against the power section of the reciprocating pump when the first end of the stud is secured to the power section and the second loading end of the sleeve receives a fastener tightening a flange of the cylinder section pressed against the sleeve.
 7. The stay rod assembly of claim 6, wherein the fastener on the second end of the stay rod compresses the sleeve by a predetermined distance.
 8. The stay rod assembly of claim 7, wherein the predetermined distance is between about 0.02 inches to about 0.05 inches.
 9. The stay rod assembly of claim 1, further comprising a first stress release groove between the first end and the shoulder, and a second stress release groove between the middle portion and the second end, wherein the first stress release groove and the second stress release groove each includes a curved cross section.
 10. The stay rod assembly of claim 1, wherein the sleeve further comprises at least one visual groove indicating a correct orientation for assembling the sleeve onto the stud.
 11. The stay rod assembly of claim 1, wherein the stay rod assembly experiences cycling stresses having a maximum stress, a minimum stress, and a difference between the maximum stress and the minimum stress, wherein the difference is no more than about 20% of the maximum stress.
 12. A reciprocating pump assembly comprising: a power section having a power source to reciprocate a plunger; a cylinder section having a chamber to receive the reciprocating plunger; and a stay rod assembly securing the cylinder section to the power section, the stay rod assembly comprising: a stud having a first end, a second end, a middle portion extending between the first end and the second end, and a shoulder between the first end and the middle portion; and a sleeve surrounding the stud, the sleeve having a first loading end adjacent the shoulder and a second loading end adjacent the second end of the stud, wherein the sleeve is configured to be pre-compressed and to pre-tension the stud for reducing cycling stresses.
 13. The reciprocating pump assembly of claim 12, wherein the middle portion between the shoulder and the second end further comprises a plurality of fluted channels extending at least partially therebetween.
 14. The reciprocating pump assembly of claim 12, wherein the first end of the stud comprises threads for fastening onto the power section of the reciprocating pump, and the second end of the stud comprises threads to receive a nut.
 15. The reciprocating pump assembly of claim 12, wherein the first loading end of the sleeve abuts the power section of the reciprocating pump when the first end of the stud is secured to the power section and the second loading end of the sleeve abuts the cylinder section.
 16. The reciprocating pump assembly of claim 15, further comprising a fastener on the second end of the stay rod to compress the sleeve by a predetermined distance.
 17. The reciprocating pump assembly of claim 12, further comprising a stress release groove extending at least partially around the stud at a position between the first end and the shoulder.
 18. The reciprocating pump assembly of claim 12, further comprising a stress release groove extending at least partially around the stud at a position between the middle portion and the second end.
 19. The reciprocating pump assembly of claim 12, wherein the stay rod assembly experiences cycling stresses having a maximum stress, a minimum stress, and a difference between the maximum stress and the minimum stress, wherein the difference between the maximum stress and the minimum stress is less than about 20% of the maximum stress.
 20. A method for assembling a reciprocating pump assembly, the pump assembly having a power section and a cylinder section, the power section reciprocatingly positioning a plunger toward and away from the cylinder section, the method comprising: securing a first end of a stud to the power section of the reciprocating pump, wherein the stud includes a middle portion extending between the first end and a second end and a shoulder positioned between the first end and the middle portion; inserting a sleeve over the stud and pressing a first loading end of a sleeve against the power section such that the sleeve surrounds the middle portion of the stud and the first loading end is adjacent the shoulder of the stud; inserting the second end of the stud through a flange of the cylinder section of the reciprocating pump assembly such that the second loading end of the sleeve abuts the flange of the cylinder section; and securing a fastener onto the second end of the stud such that the fastener compresses the flange and the sleeve by a predetermined distance.
 21. The method of claim 20, wherein the predetermined distance is between about 0.02 inches to about 0.05 inches.
 22. The method of claim 20, wherein the first end and the second end of the stud comprises threads for respectively fastening to the power section and the fastener.
 23. The method of claim 20, wherein the stud further comprises a first stress release groove extending at least partially around the stud and located between the first end and the shoulder, and a second stress release groove extending at least partially around the stud and located between the middle portion and the second end, wherein the first stress release groove and the second stress release groove each includes a corresponding gradually varying rounding radius.
 24. The method of claim 20, wherein the stud and the sleeve experience cycling stresses having a maximum stress, a minimum stress, and a difference between the maximum stress and the minimum stress, and the difference between the maximum stress and the minimum stress is less than about 20% of the maximum stress. 